Wireless communication networks have been widely deployed and utilised for the past decade or more and are expected to continue to evolve in the future to provide communication services (and content types) such as, for example, voice communication, VoIP, video, packet data, messages, multimedia, broadcast, multicast, etc. Wireless communication networks may be multiple-access networks, and types of multiple-access networks include Time Division Multiple Access (TDMA) networks, Code Division Multiple Access (CDMA) networks, Frequency Division Multiple Access (FDMA) networks, Orthogonal FDMA (OFDMA) networks, and Single Carrier FDMA (SC-FDMA) networks. A wireless communication network may also be referred to as wide area network (WAN).
A wireless communication network may include a number of base stations that can provide wireless connectivity supporting communication between a number of user equipments (UEs). A UE may communicate with a base station via the uplink (UL) and downlink (DL) channels. Downlink (also called the forward link) refers to transmissions from a base station to a UE, and uplink (also called the reverse link) refers to transmissions from a UE to a base station. Recently, there has been a trend to make available and utilise spectrum allocated to cellular networks for direct communication between UEs; that is, between one UE and another UE, or among a group of UEs within a local vicinity. This is often referred to as device-to-device or “D2D” communication (or simply “direct communication”). UEs which support direct communication may be referred to as D2D-UEs.
Direct communication may have advantages over normal cellular network communication (in the latter communications between UEs are sent via the one or more base stations). Direct communication may also coexist with the overlaid cellular network in order to improve overall system spectral efficiency. In other words, direct communication and normal cellular network communication may be supported concurrently (i.e. so that both can occur within a given wireless communication network). D2D-UEs are therefore generally capable of both cellular network communication and direct communication.
In comparison to cellular network communication, D2D communication may (at least in certain circumstances) be better suited for communicating small amounts of payload information with low overhead. Additionally, direct communication may be well suited to efficient communications in a small or localised region where channel conditions between the various devices/D2D-UEs are good or at least better than the channel condition that exists between the devices/D2D-UEs and the base station(s). Furthermore, D2D communication may allow an overlaid cellular network to offload traffic going through the base station(s) by allowing multiple paired or grouped devices/D2D-UEs to perform direct communication (i.e. between one another) sharing the same allocated block of cellular network resource. However, D2D communication may also have some limitations in comparison with cellular network communication, such as in relation to discovery, discovery range, direct communication range and change (e.g. channel change) due to device/D2D-UE mobility.
In typical cellular network communications, an access point (e.g. a base station) will generally have an antenna situated at a favourable site (e.g. with a high antenna location elevation, low obstruction, etc). The access point (base station) serves as an intermediary for UEs within its coverage. In addition, each access point (base station) is coupled via a backhaul network to other access point(s) (base station(s)) at other locations thereby providing a very large communications range. In contrast, in wireless direct communication, devices/D2D-UEs that may be interested in direct communication with each other may have less than favourable channel conditions until they are very close. This is due, for example, to their usually low antenna position which is often subjected to high levels of obstructions. As a result, the range and/or reliability of discovery between devices for direct communication can be limited. Furthermore, in typical cellular network communications, a UE knows its servicing access node (base station), and the servicing access node (base station) provides known resources for the UE to access the network and it centrally resolves collisions arising from simultaneous requests for network access. In contrast, in wireless direct communication, each device/D2D-UE behaves randomly and there is no device which performs a role as central device to resolve collisions which may occur in device discovery. This has tended to negatively impact the effectiveness and/or viability of direct communication, including when used to compliment/supplement normal cellular network communication.
It would therefore appear to be desirable to help improve discovery operations for direct communication.
It is to be clearly understood that mere reference herein to previous or existing apparatus, products, systems, methods, practices, publications or other information, or to any problems or issues, does not constitute an acknowledgement or admission that any of those things individually or in any combination formed part of the common general knowledge of those skilled in the field, or that they are admissible prior art.